Methodology for placement based on circuit function and latchup sensitivity

Abstract

A structure, apparatus and method for circuits to minimize sensitivity to latch. The method includes, for example, identifying element density of at least one functional circuit block and element attributes of elements associated with the at least one functional circuit block. An element density function parameterized from the element attributes is formed. The placement of the at least one functional circuit block is modified relative to other functional circuit blocks based on the element density function to substantially eliminate latching effects in a circuit.

The invention claimed is: 
     
       1. A method of optimizing latchup robustness in integrated circuits comprising the steps of:
 identifying element density of at least one functional circuit block; 
 identifying element attributes of elements associated with the at least one functional circuit block; 
 forming an element density function parameterized from the element attributes; 
 modifying placement of the at least one functional circuit block relative to other functional circuit blocks based on the element density function to substantially eliminate latching effects in a circuit; and 
 controlling a global placement of the at least one functional circuit block relative to injection sources in order to optimize chip performance. 
 
     
     
       2. The method of  claim 1 , wherein the element density is at least one of PFET density and NFET density. 
     
     
       3. The method of  claim 2 , wherein the modifying placement step includes:
 placing the NFET density of a given functional circuit block away from a source of undershoot; and 
 placing the PFET density of a given functional circuit block away from a source of overshoot. 
 
     
     
       4. The method of  claim 1 , wherein the step of identifying element attributes includes identifying at least one of sensitive to temperature, power, overshoot, undershoot, external sources, injection mechanisms, element pair density and strength and latchup resiliency, orientation and form factor in the at least one functional circuit block and spatial density. 
     
     
       5. The method of  claim 1 , further comprising providing decoupling capacitor elements to fill space or add capacitance to eliminate propagation adjacent an injection source to avoid propagation of latchup or soft latchup. 
     
     
       6. The method of  claim 1 , wherein prior to the modifying placement step, the method further comprising the steps of determining at least one of:
 (i) orientation and placement of an injecting source; 
 (ii) distance between an ESD element and adjacent region of high pnpn density; 
 (iii) form factors of the at least one functional circuit block; 
 (iv) guard ring utilization between adjacent functional circuit blocks; 
 (v) NPN density—Number of npn per unit area; 
 (vi) NPN parameter strength (current gain); 
 (vii) PNP density—Number of pnp per unit area; 
 (viii) PNP parameter strength (pnp current gain); 
 (ix) parameterization of the NPN density as a function of strength parameters statistics; 
 (x) parameterization of the PNP density as a function of the strength parameters statistics; 
 (xi) PNPN density; and 
 (xii) PNPN parameter strength. 
 
     
     
       7. The method of  claim 1 , wherein identifying element density of the at least one functional circuit block includes identifying element density at a perimeter of the at least one functional circuit block to determine a surface density function on the perimeter. 
     
     
       8. The method of  claim 1 , wherein the modifying placement step includes spacing the at least one functional circuit block apart from the other functional circuit blocks to reduce coupling strength between elements associated therewith. 
     
     
       9. The method of  claim 1 , further comprising at least one of:
 predicting a latchup tolerance; 
 predicting latchup within the at least one functional circuit block; 
 utilizing latchup as a design placement criteria for global interactions of the at least one functional circuit block relative to another functional circuit block; 
 identifying a form factor and either spatial densification or layout optimization of the at least one functional circuit block in order to influence propagation of latchup throughout the chip; and 
 evaluating a global latchup of injector-to-block distance and a functional block latchup functional. 
 
     
     
       10. A method comprising the steps of:
 identifying element density of at least one functional circuit block; 
 identifying element attributes of elements associated with the at least one functional circuit block; 
 forming an element density function parameterized from the element attributes; 
 modifying placement of the at least one functional circuit block relative to other functional circuit blocks based on the element density function to substantially eliminate latching effects in a circuit; and 
 determining magnitude of latchup sensitivity of a specific circuit by:
     F ==β NPN β pnp /[( I   DD   +I   RW β npn )/( I   DD   −I   RW −/ RS (β npn   +1 )/(β npn ))]
 
 
 wherein when (i) F is less than 1, then latchup does not occur and (ii) F>1 then latchup will occur. 
 
     
     
       11. The method of  claim 10 , wherein:
 a relative distance between a location of an injecting source and a collecting circuit at (i) comprising elements associated with the at least one functional circuit block is designated as a vector R r i , where an injector is at a vector position R and a collecting structure is at vector position r i ; 
 a relative distance between the location of a first circuit at (i) and a second circuit (j) of the at least one functional circuit block is designated as a vector r i r j ; 
 a spatial function is established which is a relative strength of injection source at R at the position (i); and 
 wherein a function is created where: 
 (i) if an N pnpn (F>1) of a first chip region is greater than the N pnpn (F>1) of a second chip region then the first chip region is moved farther away from the injection region; 
 (ii) if the N pnpn (F<1) of the first chip region is greater than the N pnpn (F<1) of the second chip region then the first chip region is moved closer to the injection region; and 
 (iii) if the N pnpn (F)=0 for the first chip region, then the first chip region is move closest to the injection region. 
 
     
     
       12. The method of  claim 11 , wherein an injection current strength is defined as:
     I   injection   =[I   inj ( R )/| R−r   i | 2 ]exp-{| R−r   i |( D   ζ ) 1/2 , } 
 where I injection=I RW , 
 wherein when the at least one functional circuit block contains elements whose initial state is F>1 after placement of the functional circuit block, the method further includes the steps of: 
 performing a re-optimization of local elements by changing spacing of well contact and substrate contacts associated with the elements. 
 
     
     
       13. The method of  claim 11 , wherein placement is chosen based on peak temperature at location R. 
     
     
       14. A method comprising the steps of:
 identifying element density of at least one functional circuit block; 
 identifying element attributes of elements associated with the at least one functional circuit block; 
 forming an element density function parameterized from the element attributes; and 
 modifying placement of the at least one functional circuit block relative to other functional circuit blocks based on the element density function to substantially eliminate latching effects in a circuit, 
 wherein the element density function includes: 
 counting independent BP shapes indicating a number of pnp elements thereby determining a number of p diffusions associated with the at least one functional circuit block; and 
 counting of independent ROX shapes indicating the number of npn elements associated with the at least one functional circuit block. 
 
     
     
       15. The method of  claim 14 , further comprising determining a number of pnpn and npnp elements based on the number of npn elements and pnp elements to determine element density of the at least one functional circuit block. 
     
     
       16. A computer program product for optimizing latchup robustness in integrated circuits comprising:
 a computer usable medium having computer readable program code embodied in the medium, the computer program product having: 
 computer program for identifying element density of at least one functional circuit block; 
 computer program for identifying element attributes of elements associated with the at least one functional circuit block; 
 computer program for forming an element density function parameterized from the element attributes; 
 computer program for modifying placement of the at least one functional circuit block relative to other functional circuit blocks based on the element density function to substantially eliminate latching effects in a circuit; and 
 computer program for controlling a global placement of the at least one functional circuit block relative to iniection sources in order to optimize chip performance.